270 Animal Life and Intelligence. 



That we have such a sense of rotation has been proved 

 experimentally.* Let a man, blindfolded, sit on a smooth- 

 running turn-table. When it begins to rotate he feels that 

 he is being moved round, but if ihe rotation be continued 

 at the same rate, this feeling quickly dies away. If the 

 rotation be increased, he again feels as if he were being 

 moved round, but this again soon dies away. Further in- 

 crease gives a fresh sensation, which in turn subsides, and 

 the man may then be spinning round rapidly, and be per- 

 fectly unconscious of the fact. He is only aware that he has 

 been gently turned round a little two or three times. Now 

 let the speed of rotation be slackened. He has a sensation 

 of being gently turned round a little in the opposite direction. 

 Each time the speed is lessened he has this sense of being 

 turned the reverse way. From these experiments we see 

 that what we are conscious of is change of rate of rotation, 

 or, in technical language, acceleration, positive or negative. 



From Professor Crum Brown's paper in Nature I tran- 

 scribe, with some verbal modifications, his account of how 

 the semicircular canals enable us to feel these changes of 

 KC 



A 



Fig. 30. Diagram of semicircular canals. 



A. bony labyrinth of human ear (after Summering), c, c., the cochlea; *.c., superior 

 semicircular canal ; p.c., posterior semicircular canal ; A.c., horizontal semicircular canal ; 

 o, a, a, their swellings, or ampullae; f.o.,f.r., fenestra ovalis and rotunda (oval and round 

 windows) in the vestibule. 



B. Diagram of semicircular canal to illustrate effect of rotation. The large arrows indicate 

 the direction of the rotation. The small arrow to the left indicates the resulting flow of the 

 inner fluid into the ampulla ; that to the right, the flow of the outer fluid into the vestibule. 



motion. Let us consider the action of one canal. If the 

 head be rotated about a line at right angles to the plane of 

 the canal, with the ampulla leading, there will be a tendency 



* See a very interesting and lucid paper by Professor Crum Brown, whose 

 name is intimately connected with this subject, in Nature, vol. xl. p. 449. 



